The afterglows of gamma-ray bursts

Gamma-ray burst astronomy has undergone a revolution in the last three years, spurred by the discovery of fading long-wavelength counterparts. We now know that at least the long-duration GRBs lie at cosmological distances with estimated electromagnetic energy release of 10^51–10^53 erg, making these the brightest explosions in the Universe. In this article we review the current observational state, beginning with the statistics of X-ray, optical, and radio afterglow detections. We then discuss the insights these observations have given to the progenitor population, the energetics of the GRB events, and the physics of the afterglow emission. We focus particular attention on the evidence linking GRBs to the explosion of massive stars. Throughout, we identify remaining puzzles and uncertainties, and emphasize promising observational tools for addressing them. The imminent launch of HETE-2 and the increasingly sophisticated and coordinated ground-based and space-based observations have primed this field for fantastic growth

The afterglows of gamma-ray bursts

Gamma-ray burst astronomy has undergone a revolution in the last three years, spurred by the discovery of fading long-wavelength counterparts. We now know that at least the long duration GRBs lie at cosmological distances with estimated electromagnetic energy release of 10^51–10^53 erg, making these the brightest explosions in the Universe. In this article we review the current observational state, beginning with the statistics of X-ray, optical, and radio afterglow detections. We then discuss the insights these observations have given to the progenitor population, the energetics of the GRB events, and the physics of the afterglow emission. We focus particular attention on the evidence linking GRBs to the explosion of massive stars. Throughout, we identify remaining puzzles and uncertainties, and emphasize promising observational tools for addressing them. The imminent launch of HETE-2 and the increasingly sophisticated and coordinated ground-based and space-based observations have primed this field for fantastic growth. This overview is a combined write-up of talks given at this conference and in NASA's Goddard Space Flight Center

Three-Dimensional Phthalocyanine Metal-Catecholates for High Electrochemical Carbon Dioxide Reduction.

The synthesis of a new anionic 3D metal-catecholate framework, termed MOF-1992, is achieved by linking tetratopic cobalt phthalocyanin-2,3,9,10,16,17,23,24-octaol linkers with Fe3(-C2O2-)6(OH2)2 trimers into an extended framework of roc topology. MOF-1992 exhibits sterically accessible Co active sites together with charge transfer properties. Cathodes based on MOF-1992 and carbon black (CB) display a high coverage of electroactive sites (270 nmol cm-2) and a high current density (-16.5 mA cm-2; overpotential, -0.52 V) for the CO2 to CO reduction reaction in water (faradaic efficiency, 80%). Over the 6 h experiment, MOF-1992/CB cathodes reach turnover numbers of 5800 with turnover frequencies of 0.20 s-1 per active site

The afterglows of gamma-ray bursts

Gamma-ray burst astronomy has undergone a revolution in the last three years, spurred by the discovery of fading long-wavelength counterparts. We now know that at least the long duration GRBs lie at cosmological distances with estimated electromagnetic energy release of 10^51–10^53 erg, making these the brightest explosions in the Universe. In this article we review the current observational state, beginning with the statistics of X-ray, optical, and radio afterglow detections. We then discuss the insights these observations have given to the progenitor population, the energetics of the GRB events, and the physics of the afterglow emission. We focus particular attention on the evidence linking GRBs to the explosion of massive stars. Throughout, we identify remaining puzzles and uncertainties, and emphasize promising observational tools for addressing them. The imminent launch of HETE-2 and the increasingly sophisticated and coordinated ground-based and space-based observations have primed this field for fantastic growth

Rapid Cycling and Exceptional Yield in a Metal-Organic Framework Water Harvester.

Sorbent-assisted water harvesting from air represents an attractive way to address water scarcity in arid climates. Hitherto, sorbents developed for this technology have exclusively been designed to perform one water harvesting cycle (WHC) per day, but the productivities attained with this approach cannot reasonably meet the rising demand for drinking water. This work shows that a microporous aluminum-based metal-organic framework, MOF-303, can perform an adsorption-desorption cycle within minutes under a mild temperature swing, which opens the way for high-productivity water harvesting through rapid, continuous WHCs. Additionally, the favorable dynamic water sorption properties of MOF-303 allow it to outperform other commercial sorbents displaying excellent steady-state characteristics under similar experimental conditions. Finally, these findings are implemented in a new water harvester capable of generating 1.3 L kgMOF -1 day-1 in an indoor arid environment (32% relative humidity, 27 °C) and 0.7 L kgMOF -1 day-1 in the Mojave Desert (in conditions as extreme as 10% RH, 27 °C), representing an improvement by 1 order of magnitude over previously reported devices. This study demonstrates that creating sorbents capable of rapid water sorption dynamics, rather than merely focusing on high water capacities, is crucial to reach water production on a scale matching human consumption

The Cosmic Gamma-Ray Bursts

Cosmic gamma-ray bursts are one of the great frontiers of astrophysics today. They are a playground of relativists and observers alike. They may teach us about the death of stars and the birth of black holes, the physics in extreme conditions, and help us probe star formation in the distant and obscured universe. In this review we summarise some of the remarkable progress in this field over the past few years. While the nature of the GRB progenitors is still unsettled, it now appears likely that at least some bursts originate in explosions of very massive stars, or at least occur in or near the regions of massive star formation. The physics of the burst afterglows is reasonably well understood, and has been tested and confirmed very well by the observations. Bursts are found to be beamed, but with a broad range of jet opening angles; the mean gamma-ray energies after the beaming corrections are ~ 10^51 erg. Bursts are associated with faint ~ 25 mag) galaxies at cosmological redshifts, with ~ 1. The host galaxies span a range of luminosities and morphologies, but appear to be broadly typical for the normal, actively star-forming galaxy populations at comparable redshifts and magnitudes. Some of the challenges for the future include: the nature of the short bursts and possibly other types of bursts and transients; use of GRBs to probe the obscured star formation in the universe, and possibly as probes of the very early universe; and their detection as sources of high-energy particles and gravitational waves.Comment: An invited review, to appear in: Proc. IX Marcel Grossmann Meeting, eds. V. Gurzadyan, R. Jantzen, and R. Ruffini, Singapore: World Scientific, in press (2001); Latex file, 33 pages, 22 eps figures, style files include

The role of the emergency department in the management of acute heart failure: an international perspective on education and research

Emergency departments are a major entry point for the initial management of acute heart failure (AHF) patients throughout the world. The initial diagnosis, management and disposition - the decision to admit or discharge - of AHF patients in the emergency department has significant downstream implications. Misdiagnosis, under or overtreatment, or inappropriate admission may place patients at increased risk for adverse events, and add costs to the healthcare system. Despite the critical importance of initial management, data are sparse regarding the impact of early AHF treatment delivered in the emergency department compared to inpatient or chronic heart failure management. Unfortunately, outcomes remain poor, with nearly a third of patients dying or re-hospitalised within 3 months post-discharge. In the absence of robust research evidence, consensus is an important source of guidance for AHF care. Thus, we convened an international group of practising emergency physicians, cardiologists and advanced practice nurses with the following goals to improve outcomes for AHF patients who present to the emergency department or other acute care setting through: (a) a better understanding of the pathophysiology, presentation and management of the initial phase of AHF care; (b) improving initial management by addressing knowledge gaps between best practices and current practice through education and research; and (c) to establish a framework for future emergency department-based international education and research

GRB 000418: A Hidden Jet Revealed?

We report on optical, near-infrared and centimeter radio observations of GRB000418 which allow us to follow the evolution of the afterglow from 2 to 200 days after the gamma-ray burst. In modeling these broad-band data, we find that an isotropic explosion in a constant density medium is unable to simultaneously fit both the radio and optical data. However, a jet-like outflow with an opening angle of 10-20 degress provides a good description of the data. The evidence in favor of a jet interpretation is based on the behavior of the radio light curves, since the expected jet break is masked at optical wavelengths by the light of the host galaxy. We also find evidence for extinction, presumably arising from within the host galaxy, with A(V)=0.4 mag, and host flux densities of F_R=1.1 uJy and F_K=1.7 uJy. These values supercede previous work on this burst due to the availability of a broad-band data set allowing a global fitting approach. A model in which the GRB explodes into a wind-stratified circumburst medium cannot be ruled out by these data. However, in examining a sample of other bursts (e.g. GRB990510, GRB000301C) we favor the jet interpretation for GRB000418.Comment: ApJ, submitte

Stress corrosion cracking of candidate waste container materials; Final report

Six alloys have been selected as candidate container materials for the storage of high-level nuclear waste at the proposed Yucca mountain site in Nevada. These materials are Type 304L stainless steel (SS). Type 316L SS, Incoloy 825, phosphorus-deoxidized Cu, Cu-30%Ni, and Cu-7%Al. The present program has been initiated to determine whether any of these materials can survive for 300 years in the site environment without developing through-wall stress corrosion cracks. and to assess the relative resistance of these materials to stress corrosion cracking (SCC)- A series of slow-strain-rate tests (SSRTs) and fracture-mechanics crack-growth-rate (CGR) tests was performed at 93{degree}C and 1 atm of pressure in simulated J-13 well water. This water is representative, prior to the widespread availability of unsaturated-zone water, of the groundwater present at the Yucca Mountain site. Slow-strain-rate tests were conducted on 6.35-mm-diameter cylindrical specimens at strain rates of 10-{sup {minus}7} and 10{sup {minus}8} s{sup {minus}1} under crevice and noncrevice conditions. All tests were interrupted after nominal elongation strain of 1--4%. Scanning electron microscopy revealed some crack initiation in virtually all the materials, as well as weldments made from these materials. A stress- or strain-ratio cracking index ranks these materials, in order of increasing resistance to SCC, as follows: Type 304 SS < Type 316L SS < Incoloy 825 < Cu-30%Ni < Cu and Cu-7%Al. Fracture-mechanics CGR tests were conducted on 25.4-mm-thick compact tension specimens of Types 304L and 316L stainless steel (SS) and Incoloy 825. Crack-growth rates were measured under various load conditions: load ratios M of 0.5--1.0, frequencies of 10{sup {minus}3}-1 Hz, rise nines of 1--1000s, and peak stress intensities of 25--40 MPa{center_dot}m {sup l/2}